The weft thread presenting and clamping apparatus includes several presenting levers. A weft thread clamp is mounted on the free end of each of the levers. Each lever can be moved by suitable means into a reference plane established for feeding or presenting a weft thread to a weft thread insertion device and can be swung or pivoted in the reference plane about a pivot axis, from a home position into at least one operating position, for example, into a so-called presenting position for presenting a weft thread to the gripper of a gripper loom. The particular weft thread to be presented to the weft thread insertion device is clamped between a first and a second clamp element in a corresponding weft thread clamp of the respective presenting lever.
The clamping and releasing functions of the clamp elements of the weft thread clamp are carried out passively under the constant elastic clamping tension of the clamp elements, as follows. The respective weft thread clamp automatically or necessarily takes up and holds the weft thread that has been inserted into the weaving shed, as this thread is beat-up against the binding edge, when the respective associated presenting lever is in an intermediate position between the home position and the operating position. Thereby, the constant elastic clamping tension of the clamp elements relative to each other holds the weft thread clamped therebetween. Disadvantageously, however, this process does not ensure that the weft thread has been clamped reliably and that the clamping can also be maintained independently of the point of time of the presenting of the weft thread. Also, the time at which the thread is to be released is not precisely definable.
The following example illustrates the above described disadvantages. A weft thread presenting and clamping apparatus according to the German Utility Model DE 297 16 310 U1, or according to allowed U.S. application Ser. No. 09/150,355 respectively, has a pluraity of weft thread presenting levers, e.g., six levers. A particular weft thread that is clampingly held in a respective thread clamp is to be presented to the weft insertion gripper only during some of the weft insertion operations, and not during others, for example when a different color thread held by a different one of the clamps is to be inserted. As a result, the respective presenting lever is moved up and down a number of times into different vertical positions relative to the reference plane, while holding the clamped weft thread. These movements of the presenting lever can result in the weft thread being unintentionally pulled from the clamp and, consequently, can lead to an interruption of the weaving process.
A further disadvantage of the known thread clamps is that the weft thread, when being picked up by the gripper, must be pulled out of the clamp, which still applies the constant clamping tension to the thread. This process can damage the structure of the weft thread and lead to unravelling of the thread end, resulting in single filaments of the thread remaining in the clamp, or in breakage of the weft thread.